Electrical coil and method of making the same



Patented Aug. 12, 1941 ELECTRICAL COIL AND METHOD OF MAKING THE SAME Theodore F. Rosing, Whitefish Bay, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application August 21, 1939, Serial No. 291,164

7 Claims.

This invention relates to electrical coils and the method of making the same. relates more particularly to electrical coils which are impregnated with an insulating substance or compound, such as China-wood oil and other preparations, which is introduced into the coil in a liquid state and which is subsequently solidifled, as by heating.

In insulated electrical coils of the aforementioned character it is highly desirable that all of the interstices or voids within the coil,be completely filled with the impregnating substance so as' to provide a coil of high dielectric strength and to preclude the entrance of any moisture or deleterious vapors or gases into the finished coil. The impregnating substance is accordingly preferably introduced into the coil in a liquid state to facilitate the flow thereof into the coil to fill the same completely. It is further desired to prevent drainage or loss of any of the liquid impregnating substance from the interior of the coil following impregnation thereof,

Accordingly one of the principal objects of the invention is to provide an electrical coil of the aforementioned character which is so constructed as to provide for introduction readily of the liquid impregnating substance into the coil and to insure complete retention of such substance within the coil prior to its solidification.

Another object is to provide an improved electrical coil of highdielectric and mechanical strength which is impervious to moisture and to deleterious vapors and gases.

Another object is to provide an electrical coil of the aforementioned character which is so constructed as to insure a relatively thick and adequately strong covering of insulating material surrounding the turns of wire in the coil.

Another object is to provide an electrical coil of the aforementioned character having end plates or washers of sheet insulating material which are securely attached to the coil in a novel and economical manner.

Another object is to provide a coil of the aforementioned or similar character wherein the wiring terminals are rigidly and permanently secured to one or certain of the insulating plates associated therewith.

Another object is to provide a simple, economical and effective method of making an electrical coil of the aforementioned character.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates certain The invention embodiments of the invention which will now be described, it being understood that the invention is susceptible of embodiment in other forms without departing from the scope of the appended claims.

In the drawing,

Figure 1 is an end view of an electrical coil embodying the invention,

Fig. 2 is a side elevational view of the coil shown in Fig. 1,

Fig. 3 is an enlarged fragmentary sectional view of the coil on line 3 of Fig. 1,

Fig. 4 is an enlarged fragmentary end view of the coil shown in Fig. 1 before impregnation thereof, one of the end plates being shown as broken away to show the interior of the coil,

Fig. 5 is a fragmentary sectional view on line 5-5 of Fig, 4,

Fig. 6 illustrates in modified form an electrical coil which embodies the invention,

Fig. 7 is a side elevational view of the coil shown in Fig. 6, parts thereof being shown in section to illustrate the wiring terminal arrangement.

Referring first to Figs. 1 to 5 of the drawing, the numeral i (Figs. 1 and 2) designates generally anelectrical coil constructed in accordance with the present invention and comprising a tubular insulating core member 2 of cardboard or other suitable material upon which is applied or wound a serving of an insulated conductor 3. An -enameled conductor of known form is preferably employed, especially in coils of small size requiring a great number of turns, but any other suitable insulated conductor may, of course, be employed. A wrapping of relatively thin insulating material 4, such as glassine paper is preferably applied over the serving of insulated conductor. Alternate layers of servings of insulated electrical conductor 3 and wrappings of thin insulating material 4 are wound upon the core 2 until the desired number of turns of conductor to provide the required electrical characteristics for the coil have been applied to the core whereupon a number of layers of a suitable fabric tape 5 are wound about the coil. It should be noted that an outside layer of the insulating material 4 peripherally surrounds or encloses the coil.

Tubular core member 2 and the wrappings of insulating material 4 are preferably of a length to extend some 'distance beyond the layers of conductor 3 at each end of the coil. A relatively thick, viscous, preferably air hardening, filler material, such as cellulose acetate dissolved in acetone, is applied to the ends of the coil as indiother end being covered except for a radial strip or space, as shown at l in Fig. 4.

End plates or washers 8 and 9 formed of stiff paper or other suitable insulating material are cemented to the'opposite ends of the coil, respectively, by being applied to the cellulose acetate filler material 6 while the same is still in a wet or plastic state. Thus it will be apparent as shown in Figs. 4 and that a very small opening or capillary passage iii of a width corresponding to the width of the uncovered radial strip 1 will be formed between one end, respectively, of each of the paper wrappings 4 and core member 2 and the inner surface of one of the insulating washers, shown in the drawing as washer 8. Passage ID is open at its opposite-ends to the periphery of the coil structure and to the inner surface of the core member 2, respectively, and communicates with each of the spaces between the wrappings l as shown in Fig, 5.

In the coil shown in Figs. 1 and 2 the ends of the conductor are'hrought out to the outer circumference of the coil and secured to the vertically disposed legs of the L-shaped wiring terminal members H and I2, respectively, the horizontally disposed legs of which are provided with binding screws to facilitate connection of the coil in an electric circuit. Terminal members ii and I2 are rigidly secured to the outer circumference of coil .l by having their vertically disposed legs tightly wrapped beneath the layers of tape 5 (Fig. 2).

After the coils are assembled they are preferably wrapped with stripping tape and are thereafter heated in an oven or in the tank in which they are to be impregnated to drive off any moisture which may be present in the coils. With the coils in the impregnating tank the latter is impregnating substance which may have adhered thereto. The coils are then dipped into a'suitable insulating varnish which is baked to form a continuous moisture impervious coating l4 over the exterior surfaces of the coil structure.

The modified-form of coil I5 shown in Figs. 6

and '7 may be constructed substantially like coil 1 binding screw 22 which is adapted 'to thread into bushing 20. Bushings 20 are adapted to penetrate the openings in washers 2| and spaced openings, respectively, in end plate l'l. -Each of said bushings is provided with a relatively narrow flange at its upper end between which and a washer 2! one of the wire leads 23, 23 of coil i5 is clamped, the wire being looped around the shank of bushing 20. Washers 2i rest upon the upper surface of end plate H.

The lower end of each of said bushings 20 is spun or upset over the lower surface of end plate I! as shown in Fig. '7 to rigidly and permanently secure the leads 23 to the terminal members and the latter to said end plate. The insulated wire leads 23, 23 from coil IE to terminal members l8 and i9, respectively, are further covered, as indicated, with insulating mate sealed and evacuated to a predetermined degree thus evacuating substantially all of the air in the coils. While the evacuated condition of the tank is maintained the liquid impregnating substance is introduced therein until the coils are covered to the required depth,-the depth of the liquid being preferably such as to completely immerse the coil structure. A predetermined relatively high degree of pressure is then preferably applied to the surface of the liquid in the tank as by introducing a gas, such as air or carbon dioxide under pressure, to insure complete impregnation of the coils.

It should be noted that with the coils evacuated and with the liquid surface subjected to the aforementioned pressure the impregnating substance will penetrate the stripping tape and the fabric covering 5 and will pass into the interior of the coil through the capillary passage id filling the spaces between the insulating wrappings Cl and between the turns of wire 3. Following impregnation of the coils the pressure on the surface of the liquid is removed and the impregnating tank opened to the atmosphere. The excess of the liquid in the tank over that required for impregnation of the coils is drawn ofi, allowing the liquid on the exterior surfaces of the coils to drain. The capillary passage l0, however, provides against drainage of any of the liquid impregnating substance from the interior of the coil.

The coils thereafter are baked at a relatively high degree of temperature for a suilicient length of time to solidify'the impregnating substance. The solidified impregnating substance is indirial which may be partly hardened impregnating substance and partly baked insulating varnish, resulting from the aforedescribed impregnating and varnish dipping operations.

Various modifications of the wiring terminal arrangement shown in Figs. 6 and 7 will suggest themselves to those skilled in the art. For example, it may be desired to substitute for the circular washer l6 an end plate similar to i"! whereby to provide for mounting one of said wiring terminal members on each of said end plates.

What I claim as new and desired to secure by Letters Patent is:

1. As an article of manufacture, an electrical coil structure comprising a tubular insulating core, a Winding comprising a plurality of alternate wound layers of an insulated electrical conductor and sheet insulating material on said core, said sheetinsulating material and said core being of a length to at least coextencl with the layers of said conductor at the ends of said coil structure, a substantially impervious insulating covering surrounding the periphery of said wind ing, an insulating cementing material covering the entire surface of one end or" said coil structure and the major portion of the surface of the opposite end thereof excepting a radially extending passage of predetermined area which is adapted to communicate with all of the layers of said conductor, and an insulating plate secured to the last mentioned end of said coil structure by said cementing material to render said passage of capillary dimensions, said coil struc ture being adapted for impregnation with a liquid insulating substance to be solidified in situ.

2. The method of making an electrical coil which comprises winding on a core superposed layers of an insulated electrical conductor, applying to each of said layers of conductor a relatively thin sheet of insulating material, covering each end of said coil except for a radially extending portion of predetermined area on at least one end thereof with an insulating cementing material, said uncovered portion communicating with all of the spaces between said sheets of insulating material, securing to each end of said coil by said cementing material an end plate of relatively rigid insulating material to form with said uncovered portion a capillary passage, introducing a liquid impregnating substance into said coil through said capillary passage, and thereafter solidifying said impregnating substance in situ.

3. The method of producing an electrical coil structure, which comprises winding on a core a plurality of alternate layers of insulated electrical conductor and sheet insulating material, covering the opposite ends of said core and of said sheet insulating material with an insulating cementing material except for a radially extending portion or passage on at least one end of said coil structure, which passage communicates with all of the spaces between said sheets of insulating material, securing an end plate of relatively rigid insulating material to each end of said coil structure by said cementing material to render said passage of capillary dimensions, introducing into said coil structure through said passage a liquid impregnating substance to fill the spaces adjacent the turns of said conductor and between said sheets of insulating material, and thereafter solidifying said impregnating substance in situ.

4. The method of producing an electrical coil structure which comprises winding on a core a plurality of alternate layers of an insulated electrical conductor and sheet insulating material, covering the opposite ends of said core and of said sheet insulating material with an insulating cementing material except for a radially extending portion or passage on at least one end of said coil structure, which passage communicates with all of the spaces between said sheets of insulating material, securing a plate of relatively rigid insulating material to each end of said structure by said cementing material to render said passage of capillary dimensions, subjecting said structure to partial vacuum conditions within a closed container to evacuate substantially all air therefrom, introducing into the container a body of liquid insulating material for immersion of said coil structure while maintaining partial vacuum conditions, whereby at least partial impregnation of said structure through said passage by the liquid material is effected, subjecting said body or liquid material to a substantial d ree of pressure to eflect more complete impregnation of said coil structure, separating said structure from the excess of liquid material while retention thereby of its full content of said liquid material, and thereafter baking said coil structure to solidify said liquid insulating material in situ.

5. An electrical coil comprising, in combination, a .core, a winding of superposed layers of an insulated electrical conductor on said core, said winding being peripherally enclosed by a substantially impervious insulating covering, the ends of said winding being completely covered with an insulating cementing material except for a predetermined substantially radially extending area on one end thereof, and an insulating plate secured to the last mentioned end of said winding by said cementing material, whereby a relatively closely restricted substantially radial passage is provided, the spaces within said winding and said passage being filled with a liquid insulating substance solidified in situ.

6. An electrical coil structure comprising, in combination, a winding of superposed layers of insulated electrical conductor, each layer of said conductor being wrapped with a relatively thin sheet of insulating material, said sheets of insulating material and said core being of a length to at least coextend with the layers of said conductor at the ends of said coil structure, a substantially impervious covering of insulating material surrounding the periphery of said winding,

an insulating cementing material covering each end of said winding except for a substantially radial passage-forming portion of predetermined area on at least one end thereof, said portion communicating with all of the, layers of said conductor between said sheets of insulating material, and end plates of relatively rigid insulating material secured to the ends of said winding, re-

spec-tively, by said cementing material, whereby the passage formed by said portion is restricted to substantially capillary dimensions, the spaces within said coil structure and said passage being filled with a liquid insulating substance solidified in situ.

7. An electrical coil comprising, in combine.

tion, a core, a winding comprising a plurality of superposed layers of insulated electrical conductor wound on said core, a substantially impervious insulating cover peripherally enclosing said winding, insulating cementing material covering each end of said coil except for a substantially radial passage-forming portion of predetermined area on at least one end thereof, end plates of relatively rigid insulating material ends of said coil, respectively, material, whereby the w e formed by said portion is closely restricted, the within said coil and said passage being filled with a solidifled insulating substance, at least one of said end plates having portions thereof extending outwardly beyond the periphery of said coil, and spaced wiringterminal members carried upon said outwardly extended portions of said end plate having electrically and connected thereto the respective ends of, 8 11 con- I'HEODORE F. mG.

I ductor. 

